1. Field of the Invention
The present invention relates to a frostless heat exchanger and a defrosting method thereof, more particularly, to a frostless heat exchanger and a defrosting method thereof used in an air-source refrigerating system such as an airconditioner or the like, capable of preventing the efficiency of the heat exchanger from being degraded due to the creation of frost on a surface of the heat exchanger as moisture in the air condenses thereon when a surface temperature thereof drops below a freezing point of water.
2. Description of the Background Art
As refrigerating systems using a refrigerating cycle, such as a refrigerator, an air conditioner, is widely used in these days, demands for a high-efficiency refrigerating system are increasing. In general, the refrigerating system is divided into a liquid-source refrigerating system and an air-source refrigerating system. The liquid-source refrigerating system uses a liquid to cool or heat pipe(s) through which a refrigerant flows, while the air-source refrigerating system uses an air to cool or heat pipe(s) through which a refrigerant flows.
In the air-source refrigerating system, as frost formed on a surface of a heat exchanger, i.e. an evaporator, by condensation of the moisture around the heat exchanger, a degradation of the heat exchange efficiency thereof is brought about. More concretely, if a surface temperature of the evaporator drops below a freezing point of water (i.e. 0° C.), vapor around the evaporator loses its heat by the surface of the low temperature evaporator, and thus frost is formed on the surface of the evaporator, which is called “frosting”. When the frosting is continued for some time, the frost grows to be a frost layer, and the frost layer functions as an insulation layer between the cold surface of the evaporator and the air including the ambient vapor, thereby degrading heat transfer efficiency. Due to the consecutive growth of the frost layer, an area of the air passage area is reduced, which causes an air pressure to drop.
Such a pressure drop affects operational characteristics of an air blower for blowing air around the evaporator, thereby reducing an air flow quantity around the evaporator. That is, heat transfer resistance between the surface thereof and the air therearound is increased by the frost formed on the surface of the evaporator, heat transfer performance of the evaporator is degraded because the air flow therearound is reduced, and consequently, the entire refrigerating system is fatally damaged. Accordingly, a defrosting process for melting and removing the frost layer formed on the surface thereof should be performed periodically.
As researches for removing a frost layer formed on a surface of the heat exchanger has been made, various methods for removing the frost layer have been developed. Among the various methods, a high temperature gas defrosting method, an electric defrosting method, a cycle reversing defrosting method are commonly used. Herein, the high temperature gas defrosting method is a method of removing a frost layer formed on a surface of a heat exchanger by using a high temperature gas of a discharge portion of a compressor. The electric defrosting method is a method of removing the frost layer by supplying heat with a heater to the surface of the heat exchanger on which the frost layer is formed. And the cycle reversing defrosting method is a method of converting a heating cycle between a freezing cycle and a heating cycle.
However, the high temperature gas defrosting method may not attain a reliable performance when the frost layer is thick. Moreover, the electric defrosting method has demerits of requiring a separate safety device for preventing the temperature around the heat exchanger from being increased excessively caused by a long defrosting operation, while the electric defrosting method has merits of easy control and operation. The cycle reversing method also has a problem that the degree of the amenity is decreased because the freezing or heating cycle rate is reduced.
A defrosting apparatus of a refrigerator devised by Jeon Yong-duk in Korean Patent Laid-Open No. 1999-005704 discloses a method for heating a heat exchanger by passing a high temperature anitifreezing solution, however, this method is disadvantageous in that it requires a safety device for preventing an excessive raise of temperature around the heat exchanger.
Furthermore, such defrosting process bring about various problems. Firstly, as a refrigerating system cannot be operated continuously during the defrosting operation, the temperature of an evaporator is raised and thus the refrigeration performance is reduced. Additionally, as an extra heat is supplied for the defrost process, additional energy is required to remove the extra heat when the refrigerating cycle is operated again.
Generally, it is difficult to predict a proper point of time requiring defrosting process because a growth speed of a frost layer formed at a surface thereof varies according to diverse variables, such as a position of the heat exchanger, a change of a heat transfer properties by a change of vapor in the ambient air, a temperature of the ambient air, a state of a surface of the exchanger, a temperature of a surface of the exchanger, and a flow speed of the ambient air. In addition, the melted water evaporates in the air around the low temperature heat exchanger (i.e., an evaporator) and freezes again on the surface of the heat exchanger, thereby causing an additional energy loss and degradation of freezing efficiency.
Recently, methods of delaying the frosting itself, instead of defrosting process after the frosting, are being proposed. For example, there is methods to use waste heat of a compressor, or to use a high temperature refrigerant of an outlet side of a compressor is used, or to increase the air temperature by heating a refrigerant. However, as these methods require an additional apparatus and additional energy for removing the frost, they still have problems that energy is consumed excessively and performance thereof is degraded.
Also, a frostless refrigerator using absorbent devised by Yoon Jum-yul in Korean Patent Laid-Open No. 2000-0074702 discloses a method of absorbing gaseous moisture in the air introduced into an evaporator by using a solid absorbent. However, the method has problems that an apparatus for absorbing and recycling an absorbent should be additionally required, that additional power is consumed to pass both introduced air and recycling air, and that an absorbing apparatus such as a heat pump may be larger than before so as to dehumidify a large amount of air.